The production of halogenated, and particularly chlorinated hydrocarbon products by use of the so-called Deacon process, or modifications thereof is, of course, well known in the art. In general, this comprises oxyhydrochlorination, usually at a temperature of about 300.degree. C., employing a metal chloride (usually a copper chloride) catalyst impregnated on a substantially inert support such as silica or alumina or silica-alumina, or the like. It is also known that a modifying alkali metal chloride, such as potassium chloride, can be employed with the copper chloride, to suppress the volatility of copper chloride.
In the past, those skilled in the art have generally sought so-called "selective chlorination," employing a "selective catalyst." That is to say, they sought a catalyst which would provide highly selective chlorination of the hydrocarbon feedstock to a very high yield (90% or better) of a single predetermined chlorinated hydrocarbon end product, minimizing the amounts of related chlorinated hydrocarbons produced as by-products. Therefore, in the past, the efficiency of a catalyst was judged by its ability to selectively produce, for example, ethylene dichloride, in yields in excess of 90 and preferably in excess of 95%, with corresponding low conversions to other chlorinated hydrocarbons of the ethylene/ethane series, and/or carbon oxides. In the chlorination of ethylene and/or ethane, to ethylene dichloride, one would, of course, expect to also produce at least trace amounts of vinyl chloride, dichloroethylenes, trichloroethylene, trichloroethane, perchloroethylene, tetrachloroethane, and pentochloroethane.
One of the more widely employed commercial catalysts for the oxyhydrochlorination of ethylene in a fluid bed reactor will yield about a 95% conversion of ethylene to ethylene dichloride, with only trace amounts of other chlorinated hydrocarbons. This catalyst, however, can only be employed for production of ethylene dichloride since the higher temperature (above about 260.degree. C.) and/or higher HCl:ethylene ratios, required to produce a greater depth of chlorination, result in loss of fluidization, and then agglomeration of the bed. Also, the remaining 5% is predominantly carbon dioxide and carbon monoxide, which constitute easily separable, but unsalvageable by-products.
The inability to provide a depth of chlorination greater than ethylene dichloride in the oxychlorination step creates significant economic as well as environmental problems. Where the ultimate desired end product is tri- or perchloroethylene, a process which can provide oxyhydrochlorination only to ethylene dichloride will require a subsequent vapor phase chlorination to produce the desired end product. In the vapor phase chlorination, the partially chlorinated hydrocarbon and chlorine gas are reacted at 380.degree. C. to 550.degree. C. in an oxygen-free environment, with or without a catalyst (e.g., silica-alumina catalyst) to produce the highly chlorinated hydrocarbon end product and HCl. Such a combination of processes will result in an overall stoichiometric imbalance of the type described by the following equation: ##STR1##
Thus, the subsequent vapor phase chlorination reaction produces four moles of hydrochloric acid, only two of which can be recycled to the oxyhydrochlorination reactor. This creates a "captive" producer of significant quantities of hydrogen chloride, often in excess of all internal and external demand. The ratio of coproduct hydrogen chloride to chlorinated hydrocarbon end product is thus fixed, resulting in a process which is incapable of meeting changing market conditions for hydrogen chloride or chlorinated end product.
There are, of course, a wide variety of teachings in both the technical and patent literature with regard to catalysts and process modifications in the oxyhalogenation of hydrocarbons. Many of these report results in which ethylene, for example, is oxyhydrochlorinated to a depth of chlorination greater than EDC, usually through the use of a particular catalyst, but these teachings apparently cannot be successfully scaled up to a variable continuous commercial process in which the ratio of coproduct hydrogen chloride to chlorinated end product can be varied to meet changing market conditions. There have also been proposals to, in essence, fractionate the chlorinated hydrocarbon product and recycle lower chlorinated by-products back into the original OHC reactor. For example, Japanese Patent Publication 1970/34801, Ichiki et al, discloses oxychlorination or oxyhydrochlorination of ethylene at 500.degree. C. to produce a mixture which is predominantly trichloroethylene with any lower chlorinated by-products being recycled to the reactor with excess gaseous hydrogen chloride.
U.S. Pat. No. 3,642,918 to Bohl et al. discloses and claims a two-step oxychlorination and/or oxyhydrochlorination process in which a C.sub.2 hydrocarbon is oxychlorinated at a temperature of about 290.degree. C. to about 390.degree. C. to a chlorinated product of the composition C.sub.2 H.sub.x Cl.sub.y where "x" is from 1 to 3.3 and "y" is from 2.4 to 4. This first product is then fed with further oxygen to a second oxychlorination reactor which is operated at a temperature from about 370.degree. C. to 445.degree. C., inclusion of additional chlorinating agent in the second feed being optional. The real thrust of the Bohl et al teaching, however, is that the primary purpose of the second OHC reaction is not the further chlorination of the hydrocarbon molecule, but conversion of a partially chlorinated saturated hydrocarbon to a chloro olefin. Bohl did not contemplate, and can not provide, control of the production of hydrogen chloride coproduct.